1. Field
This invention relates to a method by which areas near the surfaces of apparatuses that are contaminated by many kinds of radioisotopes as the result of handling many radioisotopes in the neighborhood of accelerators, nuclear reactors, RI product manufacturing factories, nuclear fuel factories, nuclear fuel reprocessing factories, etc. are decontaminated by non-thermal laser peeling without suffering re-melting, re-diffusing or re-contaminating, and an apparatus used in that method. When a substance is irradiated with pulsed laser the pulse duration of which is extremely short, ranging from several hundred femtoseconds to less than several picoseconds, it is evaporated or removed from the irradiated region at a sufficiently faster speed than the energy dissipation of the laser, and the energy dissipation of laser-induced, laser-accelerated or laser-energized electrons and other particles, and the thermal effects of these energy dissipations are transmitted from the irradiated region to nearby areas; this phenomenon is called “non-thermal laser peeling.”
2. Description of the Related Art
Conventionally, the areas near the surfaces of apparatuses and the industrial products that are contaminated by radioisotopes are decontaminated by the following methods.    (1) The surface is physically or mechanically removed by sand blasting, grinder, surface polishing tool, and the like.    (2) The surface-deposited layer contaminated by radioisotopes is chemically corroded away with a chemical agent such as a chelating agent or an acid.    (3) The surface-deposited layer containing radioisotopes is irradiated with a continuous laser, a long-pulse laser or a short-pulse laser having a pulse duration with a period sufficiently longer than 10 picoseconds, so that it is melted or thermally evaporated.    (4) The surface-deposited layer contaminated by radioisotopes is immersed in an electrochemical etchant for electrochemical polishing.    (5) The surface-deposited layer contaminated by radioisotopes is irradiated with laser in a chlorine gas atmosphere so that the contaminants in oxide form on the metal surface are converted to a volatile or water-soluble chloride, which is then removed.    (6) The surface-deposited layer contaminated by radioisotopes is coated with a gel-decontamination agent and irradiated with laser, so that the contaminants are removed by the laser-induced chemical reaction.    (7) The surface-deposited layer contaminated by radioisotopes is physically or mechanically removed by a kind of cold-working processes which uses a water jet, with or without ceramic or metal (cast iron or iron) abrasive particles, in either a gas or water environment.